Semiconductor devices are manufactured through microfabrication by lithography using a photoresist material, but are required to be made finer by a pattern rule in accordance with the increase in integration degree and the increase in speed of LSI in recent years. In lithography using exposure to light, which is currently used as a general-purpose technique, the resolution is now approaching the intrinsic limitation associated with the wavelength of the light source.
A light source for lithography, for use in forming a resist pattern, has a shorter wavelength from a KrF excimer laser (248 nm) to an ArF excimer laser (193 nm). However, as the resist pattern is made finer and finer, there arise a problem of resolution and a problem of collapse of the resist pattern after development, and therefore there is demanded for making a resist film thinner. On the other hand, if the resist film is merely made thinner, it is difficult to achieve the resist pattern having a film thickness sufficient for processing a substrate. Accordingly, there is increasingly required a process in which not only the resist pattern but also a resist underlayer film is prepared between a resist and a semiconductor substrate to be processed and the resist underlayer film is allowed to have a function as a mask at the time of processing the substrate.
Currently, as the resist underlayer film for such a process, various ones are known. For example, in order to provide a resist underlayer film for lithography, having a selection ratio of dry etching rate close to the resist, unlike a conventional resist underlayer film having a high etching rate, there has been proposed a material for forming an underlayer film for multilayer resist process, containing a resin component having at least a substituent which releases a terminal group to form a sulfonic acid residue when a predetermined energy is applied, and a solvent (see Patent Literature 1). In addition, in order to provide a resist underlayer film for lithography, having a smaller selection ratio of dry etching rate than the resist, there has been proposed a resist underlayer film material including a polymer having a specified repeating unit (see Patent Literature 2). Furthermore, in order to provide a resist underlayer film for lithography, having a smaller selection ratio of dry etching rate than the semiconductor substrate, there has been proposed a resist underlayer film material including a polymer formed by co-polymerizing a repeating unit of acenaphthylene and a substituted or non-substituted repeating unit having a hydroxy group (see Patent Literature 3).
On the other hand, as a material for allowing such a resist underlayer film to have a high etching resistance, an amorphous carbon underlayer film is well known, which is formed by CVD using methane gas, ethane gas, acetylene gas, or the like as a raw material. However, there is demanded, in terms of process, a resist underlayer film material that can form a resist underlayer film in a wet process such as a spin coating method or screen printing.
In addition, as a material that is excellent in optical characteristics and etching resistance and that is capable of being dissolved in a solvent and being applied to a wet process, the present inventors have proposed a composition for forming an underlayer film for lithography, which contains a naphthalene formaldehyde polymer including a specified constituent unit, and an organic solvent (see Patent Literatures 4 and 5).
Meanwhile, with respect to a forming method of an intermediate layer for use in forming a resist underlayer film in a three-layer process, for example, known are a forming method of a silicon nitride film (see Patent Literature 6), and a CVD forming method of a silicon nitride film (see Patent Literature 7). In addition, as an intermediate layer material for a three-layer process, known is a material containing a silsesquioxane-based silicon compound (see Patent Literatures 8 and 9).